As the defense began presenting its case Monday, jurors heard prisoners testify that neither of the masked killers of Cpl. David McGuinn appeared to be Lee Edward "Shy" Stephens. Stephens, 32, is one of two convicted murderers accused of escaping from a cell whose lock had been jimmied and ambushing McGuinn.

More prisoners are scheduled testify Tuesday in Anne Arundel County Circuit Court, as the defense tries to cast doubt on the prosecution's contention that eyewitness testimony and the victim's blood on Stephens' clothing point to him as one of killers.

Defense witnesses said that while they had no idea who killed 42-year-old McGuinn as he performed a head count on the night of July 25, 2006, they knew that neither of his attackers could have been Stephens. Under cross-examination, the prisoners admitted they'd told police they saw nothing. They also said blood had splattered into their cells and onto their belongings, reinforcing a key defense claim that the victim's blood was spread around the area.

"They were taller," testified Phillip Custis, who is serving a 15-year sentence for drug violations. "And he was slimmer." He said Stephens' hair would have stuck out from under a gray ski mask.

Custis said that using a mirror to see the assault on the catwalk from his cell, he saw the arm swings of someone repeatedly stabbing McGuinn in the dim light. Immediately afterward, he threw his knife and cellphone — the items are contraband — off the tier, knowing an investigation would include cell searches.

Stephens is 5 feet, 9 inches tall and weighs about 180 pounds, according to arrest information on this murder charge. Other prisoners said the attackers were at least 6 feet tall, and one of them had very broad shoulders.

One prisoner testified for the prosecution at the start of the trial, identifying Stephens and co-defendant Lamarr Cornelius Harris as the attackers, but a second prisoner changed his mind and refused to speak out of fear.